In fusion energy systems (FES) neutrons are born from a burning plasma and subsequently activate surrounding system components. The photon dose rate after shutdown from the resultant radionuclides must be quantified for maintenance planning. This shutdown dose rate (SDR) is calculated by coupling neutron transport, activation analysis, and photon transport. The size, complexity, and attenuating configuration of FES motivate the use of hybrid Monte Carlo (MC)/deterministic neutron transport. The Multi-Step Consistent Adjoint Driven Importance Sampling (MS-CADIS) method can be used to optimize MC neutron transport for this purpose. This requires the formulation of an adjoint neutron source that approximates the transmutation process. In this work one such formulation is introduced which is valid when a specific set of transmutation criteria are met, referred to as the Single Neutron Interaction and Low Burnup (SNILB) criteria. These criteria are quantitatively evaluated for typical FES scenarios and are shown to be met within a reasonable margin. Groupwise Transmutation (GT)-CADIS, proposed here, is an implementation of MS-CADIS that calculates this adjoint neutron source using a series of irradiation calculations. For a simple SDR problem, GT-CADIS provides speedups of 200 ± 100 relative to global variance reduction with the Forward Weighted (FW)-CADIS method and 90,000 ± 50,000 relative to analog. When the SNILB criteria are egregiously violated, GT-CADIS modifications are proposed and are shown to provide significant performance improvements. Finally, GT-CADIS is applied to a production-level problem involving a Spherical Tokamak Fusion Nuclear Science Facility (ST-FNSF) device. This work shows that GT-CADIS is broadly applicable to FES scenarios and will significantly reduce the computational resources necessary for SDR analysis.